(1) Field of the Invention
This invention relates to novel silver halide photographic light-sensitive materials and, more particularly, to high-speed silver halide photographic light-sensitive materials which give an image having high contrast and high maximum density.
(2) Description of the Prior Art
As regards photographic silver images, the ratio of the optical density of the image to the amount of silver constituting the image per unit area is generally called the covering power. This covering power is used as a measure of the optical efficiency of the image-constituting silver. Generally, the smaller the size of the silver halide grains becomes, the greater the covering power of the photographic light-sensitive emulsion layer containing the silver halide grains becomes. On the contrary, since the greater the size of the silver halide grains becomes, the higher the sensitivity or speed of the silver halide emulsion, an emulsion containing silver halide grains of a large size is used in making a high-speed photographic light-sensitive material. It is therefore necessary to use a larger amount of silver per unit area so as to obtain a high-speed photographic light-sensitive material which gives a certain image density.
In other words, to attain both high sensitivity and maximum image density, the photographic light-sensitive material must contain a larger amount of silver salts per unit area thereof. This has been one of the problems in making a high-speed photographic light-sensitive material.
As an attempt to improve the covering power while maintaining a high sensitivity, it has been proposed to add various polymers to a high-speed emulsion containing coarser silver halide grains, as described in British Pat. Nos. 1,048,057 and 1,039,471, and U.S. Pat. Nos. 3,043,697 and 3,446,618. All the methods of these patents give only a slight and insufficient increase in covering power and further have a disadvantage in that they decrease the strength of the coated film layer. When the photographic light-sensitive material having such weak film layer is processed after imagewise exposure through an automatic developing processor of the type commonly used at present, gelatin contained in the layer partly dissolves into the developing solution or the fixing solution, sticks to the conveyor roller of the automatic developing processor, and transfers to the photographic material to produce stains on the photographic image.
U.S. Pat. Nos. 2,996,382 and 3,178,282 disclose high-speed silver halide photographic light-sensitive materials comprising surface latent image type silver halide coarse grains and internally fogged silver halide fine grains incorporated in the same or adjacent emulsion layers, which give a photographic image having increased contrast and covering power. However, these photographic light-sensitive materials tend to be fogged during development. Further they have a disadvantage in that irregular stains are producd on the photographic materials when they are processed in a developing bath and subsequently in a fixing bath without being processed in an intermediate stopping bath, using an automatic developing processor. The problem of irregular stains seems to partly originate from the formation of fog which is caused partly by the careless incorporation of the fixing solution into the developing solution.
As regards the problem of the liability to fogging in the developing process, U.S. Pat. No. 3,397,987 discloses a method for decreasing the fog formation in photographic elements, especially those sensitized with onium salts or polyalkyleneoxides, which comprises adsorbing on internally fogged silver halide grains, the development antifoggant heterocyclic nitrogen compounds containing a mercapto group which is linked to the carbon atom at .alpha.-position with respect to the nitrogen atom of the hetero ring, in the methods as described in U.S. Pat. Nos. 2,996,382 and 3,178,282.
However, almost none of the compounds disclosed in U.S. Pat. No. 3,397,987 have a good effect on the problem of the irregular stains produced in the processing by an automatic developing processor. Among these compounds, only 1-(3-capramido)-phenyl-5-mercaptotetrazole and 1-(3-pelargonamido)-phenyl-5-mercaptotetrazole had an improving effect on the problem of the irregular stains but they had a disadvantage in that the sensitivity of the photographic materials decreased with time under conditions of high temperature and humidity.